In a mobile communication system, after the data in the transmission layer are coded, the data flow in unit time is possibly different from the flow that the wireless port can bear, so rate matching is needed. The process of the rate matching is generally to interlace firstly, then combine multiple paths, and perforate or repeat. Generally speaking, null bits, also called dummy units, are introduced in the coding and rate matching. The purpose of the perforation is to remove the null bits.
A method generally used is to perform the rate matching by utilizing software or to perform single-bit serial processing by hardware. The single-bit serial processing by is hardware is as follows: reading one bit by one clock for the rate matching; if a bit is null during the perforation, not outputting the bit to a lower level; otherwise, outputting the bit to the lower level. It should not be a problem in a 3G (the Third Generation) system as the data flow in the 3G is not great, and the time delay can be relatively long. Thus, there will not be a bottleneck of the system.
In a Long Term Evolution (LTE) system, the data flow is very great, and the time delay is required to be very short. As for a system with the bandwidth of 20 MHz, in the case of 4*4 spatial multiplexing Multiple-Input Multiple-Output (MIMO), the flow of one cell will reach to 300 Mbps, and the flow of three cells will reach to 900 Mbps; and after the data are channel coded, the flow will triple. Moreover, in the LTE system, one Transmission Time Interval (TTI) is only 1 ms, and the time pre-remained for the rate matching is very little. In such case when using the conventional method, neither a single CPU nor a special hardware circuit can satisfy the requirements, and multiple CPUs or hardware circuits need to be used in parallel. As a result, the system cost rises sharply to form the bottleneck of the LTE system.